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Research about Nevada

Source-linked reports with geographic coverage including Nevada.

At least 595 records · Page 33Linked to original sources
USGS1998

Tritium in unsaturated zone gases and air at the Amargosa Desert Research Site, and in spring and river water, near Beatty, Nevada, May 1997

Elevated tritium concentrations in the unsaturated zone at the Amargosa Desert Research Site (ADRS), immediately south and west of the low-level radioactive-waste burial site south of Beatty, Nevada, have stimulated research of processes that control the transport of tritium in arid unsaturated zones. In May 1997, 58 samples were collected from 1.5 m (meters) depth within a 250 m by 250 m grid at the ADRS. Measured concentrations ranged from 16 ± 9 to 36,900 ± 300 tritium units (TU), decreasing from northeast to southwest, possibly along an ancestral Amargosa River channel. The 10 air ports at test hole UZB-2 also were sampled, including ports at 57.6, 106.4, and 108.8 m depths that had not been sampled since 1994. Of the remaining seven ports, five were sampled in 1994, 1995, and 1996, and two were sampled in 1994 and 1996. Tritium concentrations at the four ports deeper than 50 m ranged from 791 ± 15 to 1765 ± 29 TU, having increased since they were last sampled. Tritium concentrations at the six ports shallower than 50 m ranged from 367 ± 11 to 1283 ± 20 TU, and appear to have stabilized since 1996. Tritium concentration in water vapor collected from air within the creosote bush canopy was 75 ± 9 TU near test hole UZB-2 and 9 ±6 TU near the uncontaminated Fischer test hole, 3.2 km to the south. Elevated tritium concentration in air near test hole UZB-2 was attributed to plant transpiration removing water from the unsaturated zone. Nearby surface water tritium concentrations were 6.3 ± 0.4 TU at Specie Spring, 0.0 ± 0.3 TU at Lower Indian Springs and at Upper Indian Springs, and 0.8 ± 0.6 TU in Amargosa River water.

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USGS1998

Geologic map of Paleozoic rocks in the Calico Hills, Nevada Test Site, southern Nevada

The Calico Hills area in the southwestern part of the Nevada Test Site, Nye County, Nevada, exposes a core of pre-Tertiary rocks surrounded by middle Miocene volcanic strata. This map portrays the very complex relationships among the pre-Tertiary stratigraphic units of the region. The Devonian and Mississippian rocks of the Calico Hills are distinct from age-equivalent carbonate-shelf or submarine-fan strata in other parts of the Nevada Test Site. The Calico Hills strata are interpreted to have been deposited beyond the continental shelf edge from alternating silicic and carbonate clastic sources. Structures of the Calico Hills area record the compounded effects of: 1) eastward-directed, foreland-vergent thrusting; 2) younger folds, kink zones, and thrusts formed by hinterland-vergent deformation toward northwesterly and northerly directions; and 3) low-angle normal faults that displaced blocks of Middle Paleozoic carbonate strata across the contractionally deformed terrane. All of these structures are older than any of the middle Miocene volcanic rocks that were erupted across the Calico Hills.

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USGS1998

Evaluation of faults and their effect on ground-water flow southwest of Frenchman Flat, Nye and Clark counties, Nevada: a digital database

Ground-water flow through the region south and west of Frenchman Flat, in the Ash Meadows subbasin of the Death Valley ground-water flow system, is controlled mostly by faults which arrange the distribution of permeable and impermeable rocks. In addition, most permeability is along fractures caused by faulting in carbonate rocks. Large faults are more likely to reach the potentiometric surface as deep as 325 meters below the ground surface and are more likely to effect the flow path than small faults. This study concentrated on identifying large faults, especially where they cut carbonate rocks. Small faults, however, may develop as much permeability as large faults if they are penetrative and are part of an anastomosing fault_zone. The overall pattern of faults and joints at the ground surface in the Spotted and Specter Ranges is an indication of the fracture system at the depth of the water table. Most of the faults in these ranges are west-southwest-striking, high-angle faults, 100 to 3,500 meters long, with 10 to 300 meters of displacement. Many of them, such as those in the Spotted Range and Rock Valley are left-lateral strike-slip faults that are conjugate to the NW-striking right-lateral faults of the Las Vegas Valley shear zone. These faults control the ground-water flow path, which runs west-southwest beneath the Spotted Range, Mercury Valley and the Specter Range. The Specter Range thrust is a significant geologic structure with respect to ground- water flow. This regional thrust fault emplaces siliceous clastic strata into the north central and western parts of the Specter Range. These rocks act as a barrier that confines ground- water flow to the southern part of the range, directing it southwestward toward springs at Ash Meadows. These siliceous clastic aquitard rocks and overlying Cenozoic deposits probably also block westward flow of ground-water in Rock Valley, diverting it southward to the flow path beneath the southern part of the Specter Range.

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USGS1998

Oreshoot zoning in the Carlin-type Betze orebody, Goldstrike Mine, Eureka County, Nevada

Field and laboratory investigations of the giant Betze gold orebody, the largest Carlin-type deposit known, in the north-central Carlin trend, Nevada document that the orebody is composed of individual high-grade oreshoots that contain different geologic, mineralogic, and textural characteristics. The orebody is typical of many structurally controlled Carlin-type deposits, and is hosted in thin-bedded, impure carbonate or limy siltstone, breccia bodies, and intrusive or calc-silicate rock. Most ores in the Betze orebody are highly sheared or brecciated and show evidence of syndeformational hydrothermal deposition. The interplay between rock types and pre- and syn-structural events accounts for most of the distribution and zoning of the oreshoots. Hydrothermal alteration is scale dependent, either in broad, pervasive alteration patterns, or in areas related to various oreshoots. Alteration includes decarbonatization (~decalcification) of carbonate units, argillization (illite-clay), and silicification. Patterns of alteration zoning in and surrounding the Betze orebody define a large porous, dilated volume of rock where high fluid flow predominated. Local restriction of alteration to narrow illite- and clay-rich selvages around unaltered marble or calc-silicate rock phacoids implies that fluid flow favored permeable structures and deformed zones. Gold mainly is present as disseminated sub-micron-sized particles, commonly associated with Asñrich pyrite, although one type of oreshoot contains micron-size free gold. Oreshoots form a three-dimensional zoning pattern in the orebody within a WNW-striking structural zone of shearing and shear folding, termed the Dillon deformation zone (DDZ). Main types of oreshoots are: (1) rutile-bearing siliceous oreshoots; (2) illite-clay-pyrite oreshoots; (3) realgar- and orpiment-bearing oreshoots; (4) stibnite-bearing siliceous oreshoots; and (5) polymetallic oreshoots. Zoning patterns result from paragenetically early development of illite-clay-pyrite oreshoots during movement along the DDZ, and subsequent silicification and brecciation, associated with formation of the realgar- and orpiment-bearing, and stibnite-bearing oreshoots. Additional shear movement along the DDZ followed. Polymetallic oreshoots, which contain minerals rich in Hg, Cu, Zn, Ag, and native Au, were the last ores to form and overprint most earlier oreshoots. Ore textures, gouge, phyllonitic rock, alteration style, and previously documented isotopic and fluid-inclusion data, all indicate a weakly to moderately saline fluid that ascended and cooled during structural displacements. Changing conditions, due to water-wall rock reactions and P-T changes during deformation, are probably responsible for fluid variation that resulted in zoning of the different oreshoots during dynamic interaction of the Au-bearing fluid with the wall rock. This investigation indicates that isolated As-, Sb-, and Hg-rich ores are separate parts of a larger single gold system. This large gold system was contemporaneous with post-Jurassic brittle-ductile deformation, on the basis of deformed mineralized pods of the Jurassic Goldstrike pluton, and large-scale hydrothermal flow, and together they appear to be an integral part of the formation of some Carlin-type gold deposits in north-central Nevada.

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USGS1998

Digital geologic map of the Thirsty Canyon NW quadrangle, Nye County, Nevada

This digital geologic map compilation presents new polygon (i.e., geologic map unit contacts), line (i.e., fault, fold axis, dike, and caldera wall), and point (i.e., structural attitude) vector data for the Thirsty Canyon NW 7 1/2' quadrangle in southern Nevada. The map database, which is at 1:24,000-scale resolution, provides geologic coverage of an area of current hydrogeologic and tectonic interest. The Thirsty Canyon NW quadrangle is located in southern Nye County about 20 km west of the Nevada Test Site (NTS) and 30 km north of the town of Beatty. The map area is underlain by extensive layers of Neogene (about 14 to 4.5 million years old [Ma]) mafic and silicic volcanic rocks that are temporally and spatially associated with transtensional tectonic deformation. Mapped volcanic features include part of a late Miocene (about 9.2 Ma) collapse caldera, a Pliocene (about 4.5 Ma) shield volcano, and two Pleistocene (about 0.3 Ma) cinder cones. Also documented are numerous normal, oblique-slip, and strike-slip faults that reflect regional transtensional deformation along the southern part of the Walker Lane belt. The Thirsty Canyon NW map provides new geologic information for modeling groundwater flow paths that may enter the map area from underground nuclear testing areas located in the NTS about 25 km to the east. The geologic map database comprises six component ArcINFO map coverages that can be accessed after decompressing and unbundling the data archive file (tcnw.tar.gz). These six coverages (tcnwpoly, tcnwflt, tcnwfold, tcnwdike, tcnwcald, and tcnwatt) are formatted here in ArcINFO EXPORT format. Bundled with this database are two PDF files for readily viewing and printing the map, accessory graphics, and a description of map units and compilation methods.

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USGS1998

Water resources data, Nevada, water year 1997

Water resources data published herein for the 1997 water year comprise the following records: o Water discharge for 173 gaging stations on streams, canals and drains. o Discharge for 170 peak-flow stations and miscellaneous sites, and 6 springs. o Stage and contents for 21 lakes and reservoirs. o Water-quality data for 64 stream, lake, canal, spring, and drain sites, and 115 wells. o Precipitation totals for 36 stations. o Water levels for 34 continuous record wells, and 924 observation wells. o Water withdrawals for 14 wells Additional water-data, collected at various sites that are not part of the systematic data-collection program, are published as miscellaneous measurements. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in Nevada.

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USGS1998

Characterization of hydrogeologic units using matrix properties, Yucca Mountain, Nevada

Determination of the suitability of Yucca Mountain, in southern Nevada, as a geologic repository for high-level radioactive waste requires the use of numerical flow and transport models. Input for these models includes parameters that describe hydrologic properties and the initial and boundary conditions for all rock materials within the unsaturated zone, as well as some of the upper rocks in the saturated zone. There are 30 hydrogeologic units in the unsaturated zone, and each unit is defined by limited ranges where a discrete volume of rock contains similar hydrogeologic properties. These hydrogeologic units can be easily located in space by using three-dimensional lithostratigraphic models based on relation- ships of the properties with the lithostratigraphy. Physical properties of bulk density, porosity, and particle density; flow properties of saturated hydraulic conductivity and moisture-retention characteristics; and the state variables (variables describing the current state of field conditions) of saturation and water potential were determined for each unit. Units were defined using (1) a data base developed from 4,892 rock samples collected from the coring of 23 shallow and 8 deep boreholes, (2) described lithostratigraphic boundaries and corresponding relations to porosity, (3) recognition of transition zones with pronounced changes in properties over short vertical distances, (4) characterization of the influence of mineral alteration on hydrologic properties such as permeability and moisture-retention characteristics, and (5) a statistical analysis to evaluate where boundaries should be adjusted to minimize the variance within layers. This study describes the correlation of hydrologic properties to porosity, a property that is well related to the lithostratigraphy and depositional and cooling history of the volcanic deposits and can, therefore, be modeled to be distributed laterally. Parameters of the hydrogeologic units developed in this study and the relation of flow properties to porosity that are described can be used to produce detailed and accurate representations of the core-scale hydrologic processes ongoing at Yucca Mountain.

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USGS1998

Results from air-injection and tracer testing in the upper Tiva Canyon, Bow Ridge Fault, and upper Paintbrush contact alcoves of the Exploratory Studies Facility, August 1994 through July 1996, Yucca Mountain, Nevada

Air-injection and tracer testing were conducted in the upper Tiva Canyon, Bow Ridge Fault, and upper Paintbrush contact alcoves in the Exploratory Studies Facility at Yucca Mountain, Nevada, from August 1994 to July 1991. The study was conducted by the U.S. Geological Survey, in cooperation with the U.S. Department of Energy.

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USGS1998

The status of Moapa coriacea and Gila seminuda and status information on other fishes of the Muddy River, Clark County, Nevada

Moapa coriacea is endemic to the headwaters (Warm Springs area) of the Muddy River, Clark County, Nevada. The Warm Springs area was snorkeled and Moapa coriacea and Gila seminuda enumerated in August 1994 after a fire, and in May 1997 after a diversion dam had been removed from the downstream end. Gila seminuda had been reported in greatest abundance downstream from the Warm Springs area and we estimated the population there through mark and recapture from January to March 1995. There was a dramatic reduction in native fishes in the Warm Springs area between 1994 and 1997, coinciding with the invasion of Oreochromis aurea. Downstream from the Warm Springs area Gila seminuda was the most frequently netted species while O. aurea was relatively scarce. The fish population (native and non-native) decreased in a downstream direction; the causative factor(s) have not been identified.

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USGS1998

Hydrogeologic studies at the USGS Amargosa Desert Research Site

In 1976, the U.S. Geological Survey (USGS) began studies of unsaturated-zone hydrology in the Amargosa Desert in support of the USGS Low-Level Radioactive Waste Program. In 1983, agreements with the Bureau of Land Management and the State of Nevada established two field study areas: a 16-ha area adjacent to a waste-burial facility 17 km south of Beatty and a 0.1-ha area about 3 km farther south (fig. 1A). The study areas are collectively known as the Amargosa Desert Research Site (ADRS). Investigations at the ADRS have provided long-term benchmark information about hydraulic characteristics and soil-water movement for undisturbed conditions and for simulated waste-site conditions in arid environments. In 1995, as a result of unexpectedly finding high concentrations of tritium and carbon-14 in the unsaturated zone beneath the ADRS, the scope of research was broadened to include the study of processes affecting radionuclide transport. The ADRS was incorporated into the USGS Toxic Substances Hydrology Program in 1997. Research at the site is a multidisciplinary, collaborative effort that involves scientists from the USGS, universities, research institutes, and national laboratories. The overall objective for research at the site is to improve understanding of and methods for characterizing mechanisms that control subsurface migration and fate of contaminants in arid environments.

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